At present, the principle of the automatic paper feeding device of the known automatic shredders is same to that of the pick-up box of printers. When a stack of clean and orderly white paper is laid in the paper tray, the pick-up mechanism would feed the end of the topmost or bottommost sheet of the stack of paper to the knife edges of the shredder with devices like gears, cams, shift levers or pulleys, and this process will be repeated continuously till the stack of paper are shredded completely. As shown in FIG. 1a and FIG. 1b, the paper support board 11 is fixed aslant above the cutting blades 12, transmission devices like gears, cams, shift levers or pulleys are used to cause the pick-up roller 13 to feed paper so as to move the end 14 of each piece of paper forwards and into the cutting blades 12 in turn to be shredded. Wherein the pick-up roller 13 is a smooth belt or a rubber roller with teeth, and located above or below the paper support board 11.
There also has the known built-in auto-feed which has a pair of very complex bisecting lids, gravity press devices and a paper tray, two roller assemblies are provided under the bottom of a stack of paper and at opposing sides above and parallel to the cutter shafts, with the two roller assemblies parallel to each other and rotating towards each other at a same speed, paper would be half-folded and fed into the cutter shafts to be shredded. As shown in FIG. 2, two pick-up rollers 15 are located exactly above the central axis of the cutting blades 16, the bisecting gravity adjustment devices composed of upper pick-up rollers 17 and pressboards 18 are provided at the upper part of the paper tray, and the paper feeding movement should make sure the balanced and exact design of the paper feeding speed and the shredding speed. The outer diameters, the surface roughness and the moving speeds of the two pick-up rollers 15 should be same absolutely; and at the same time the gravities of two groups each composed of one of the upper pick-up rollers 17 and one of the pressboards 18 should also be same, then half-folding paper 19 can be achieved.
The first application discussed above is the most common, and the structure is relatively simple. Though its principle is same to that of printers, the stack of paper to be shredded by shredders is unlike the paper used in printers, has tilted corners, and has many waste files the pieces of paper of each of which are bound into a stack, thus the situation that with the automatic shredder bought to shred paper the number of paper should be chosen occurs. And there often occurs the situation that the shredder is smooth on trial when the user wants to buy it, but in normal uses paper jams and can not be taken out, and the pick-up mechanism would be broken if the paper is taken out forcely. Such a situation limits severely the application of these automatic shredders.
The latter known built-in auto-feed can better achieve the function of feeding paper, but the gravity press structure and the pick-up structure of the pair of rollers are too complicated, the pair of rollers and the cutter shafts are designed integratedly, the feeding speed and the shredding speed should be balanced precisely, and the original shredding rhythm would be disrupted when a stack of paper with pins or staples is shredded, moreover these shredders are made to be very large and costly. Thus the application of these shredders is also limited.
In addition, the sizes of the cutting blades, the strength of the cutter shaft the cutting blades are mounted on, and the load of the driving motor of one shredder restrict the largest number of paper the shredder can accommodate at a single time. For example, 3, 5, 8, 10, 12, 20 and so on are indicated on the shredder panel, then when the number of paper to be shredded is more than the above limited number, the paper can only be counted and divided into several stacks to be shredded one by one manually, even if the shredder has the function of shredding pins or staples, the pieces of paper also should be disconnected and counted to be divided into several stacks each less than the predetermined largest number to be fed. The number indicated is bigger, the size of the motor and the cutting blades are bigger, and then the cost pressure is greater.